The Haunted Halos of Andromeda and Triangulum: A Panorama of Galaxy Formation in Action

By R. Ibata, N. Martin, M. Irwin, S. Chapman, A. Ferguson, Geraint F. Lewis, A. McConnachie. 2007

323 citations recorded by the source corpus.

We present a deep photometric survey of the Andromeda galaxy, conducted with the wide-field cameras of CFHT and INT, that covers the inner 50 kpc of the galaxy and the southern quadrant out to ~150 kpc and includes an extension to M33 at >200 kpc. This is the first systematic panoramic study of this very outermost region of galaxies. We detect a multitude of large-scale structures of low surface brightness, including several streams, and two new relatively luminous (MV ∼ − 9) dwarf galaxies: And XV and And XVI. Significant variations in stellar populations due to intervening stream-like structures are detected in the inner halo, which is particularly important in shedding light on the mixed and sometimes conflicting results reported in previous studies. Underlying the many substructures lies a faint, smooth, and extremely extended halo component, reaching out to 150 kpc, whose stellar populations are predominantly metal-poor. We find that the smooth halo component in M31 has a radially decreasing profile that can be fitted with a Hernquist model of immense scale radius ~55 kpc, almost 4 times larger than theoretical predictions. Alternatively a power law with ΣV ∝ R−1.91 ± 0.11 can be fitted to the projected profile, similar to the density profile in the Milky Way. If it is symmetric, the total luminosity of this structure is ~109 L☉, again similar to the stellar halo of the Milky Way. This vast, smooth, underlying halo is reminiscent of a classical “monolithic” model and completely unexpected from modern galaxy formation models. M33 is also found to have an extended metal-poor halo component, which can be fitted with a Hernquist model also of scale radius ~55 kpc. These extended slowly decreasing halos will provide a challenge and strong constraints for further modeling.

Subfields: Astronomy and Astrophysics

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Simulations of minor mergers - I. General properties of thick discs (2008, background): “The giant stream of M31, thought to originate in the disruption of a satellite with mass ∼109M⊙, and the socalled eastern and western “shelfs” (Ibata et al. 2007), may be related given the similarities of their stellar populations.”
A Comprehensive Maximum Likelihood Analysis of the Structural Properties of Faint Milky Way Satellites (2008, background): “…few years (Zucker et al. 2004; Willman et al. 2005a,b; Belokurov et al. 2006; Martin et al. 2006; Sakamoto & Hasegawa 2006; Zucker et al. 2006a,b; Belokurov et al. 2007; Ibata et al. 2007; Majewski et al. 2007; Walsh et al. 2007a; Zucker et al. 2007; Irwin et al. 2008; McConnachie et al. 2008).”
Galactic stellar haloes in the CDM model (2009, background): “We now compare the z = 0 satellite populations of our models with trends observed in the dwarf companions of the Milky Way and M31 in order to determine a suitable choice of the fixed fraction, fMB, of the most bound DM particles selected in a given halo.”
The Masses of the Milky Way and Andromeda galaxies (2010, background): “In addition, the census of satellites around M31 has increased significantly (Zucker et al. 2004, 2007; Martin et al. 2006; Ibata et al. 2007; Majewski et al. 2007; Irwin et al. 2008; McConnachie et al. 2008) since the last studies of this type were attempted and so we have more data at our…”
Gaseous Galaxy Halos (2012, background): “…from the disk of the spiral are potentially linked to satellite accretion or interaction with a companion - e.g., M31 (Westmeier et al., 2005a; Ibata et al., 2007), NGC 891 (Oosterloo et al., 2007; Mouhcine et al., 2010), M33 (Putman et al., 2009c; Grossi et al., 2008), NGC 5055 (Battaglia et…”
THE GHOSTS SURVEY. I. HUBBLE SPACE TELESCOPE ADVANCED CAMERA FOR SURVEYS DATA (2011, unknown): “Subsequent surveys with Megacam on the Canada–France–Hawaii Telescope covered a quadrant of the halo out to ∼150 kpc with an extension to M33 at ∼200 kpc (Martin et al. 2006; Ibata et al. 2007).”
THE LUMINOSITY PROFILE AND STRUCTURAL PARAMETERS OF THE ANDROMEDA GALAXY (2011, methodology): “The extended M31 galaxy light profile with deep star counts reveals a halo component beyond Rmin 10 kpc at a brightness level μI ∼ 27 mag arcsec−2 (Figure 5; also Guha05; Ibata et al. 2007; Tanaka et al. 2010).”
The properties of warm dark matter haloes (2013, background): “Over the past decade, surveys such as SDSS (York et al. 2000), PAndAS (Ibata et al. 2007) and Pan-STARRS (Kaiser et al. 2010) have begun to probe the Local Universe in detail.”
A UNIVERSAL MASS PROFILE FOR DWARF SPHEROIDAL GALAXIES? (2009, unknown): “…8 Hernquist, L. 1990, ApJ, 356, 359 Ibata, R. A., Gilmore, G., & Irwin, M. J. 1995, MNRAS, 277, 781 Ibata, R. A., & Irwin, M. J. 1997, AJ, 113, 1865 Ibata et al. 2007, ApJ, 671, 1591 Illingworth, G. 1976, ApJ, 204, 73 Irwin, M., & Hatzidimitriou, D. 1995, MNRAS, 277, 1354 Irwin et al. 2007, ApJ,…”
THE DUAL ORIGIN OF STELLAR HALOS (2009, methodology): “Ibata et al. (2007), using number count maps, have shown that a large fraction of the halo of M31 appears to be rather smooth.”
THE LARGE-SCALE STRUCTURE OF THE HALO OF THE ANDROMEDA GALAXY. I. GLOBAL STELLAR DENSITY, MORPHOLOGY AND METALLICITY PROPERTIES (2013, unknown): “The aim of the present paper is to update and complement an earlier contribution on this subject (Ibata et al. 2007, hereafter paper I).”
PRE-REIONIZATION FOSSILS, ULTRA-FAINT DWARFS, AND THE MISSING GALACTIC SATELLITE PROBLEM (2008, background): “Recent surveys of M31 (Martin et al. 2006; Ibata et al. 2007) have covered approximately a quarter of the space around the M31 spiral.”
Tracing Galaxy Formation with Stellar Halos. II. Relating Substructure in Phase and Abundance Space to Accretion Histories (2008, methodology): “…first out to distances of ∼ 50 kpc (Ferguson et al. 2002) and recently expanded to explore one quarter of the galaxy out to ∼ 150kpc from its center (Ibata et al. 2007) , were put together by plotting overdensities in the number of red stars selected using broadband filters to have the right…”
The stellar halo of the Galaxy (2008, background): “Our external point of view has allowed the study of this halo in a much more global fashion (Ibata et al. 2007), and has provided spectacular images as shown in Figure 16.”
Cosmological simulations of the formation of the stellar haloes around disc galaxies (2011, methodology): “4, Pritchet & van den Bergh (1994) used the observations of the Milky Way globular cluster 47 Tuc for the conversion, while Ibata et al. (2007) and Gilbert et al. (2009a) shifted their data vertically to map onto the profile Pritchet & van den Bergh (1994) at radii of ≈ 10− 30 kpc.”
UPDATED NEARBY GALAXY CATALOG (2013, background): “…2009) HI surveys of the northern sky, and as a result of systematic search – 6 – for dwarf satellites of extremely low luminosity, resolved into stars, around the Milky Way (Willman et al. 2005, Belokurov et al. 2006), M 31 (Ibata et al. 2007, Martin et al. 2009) and M 81 (Chiboucas et al., 2009).”
Thin, thick and dark discs in ΛCDM (2008, background): “Indeed, this could provide an explanation for the extended disc seen in Andromeda (Ibata et al. 2005 and Section 1).9 From Section 2, we expect ∼15 such low inclination, low mass, mergers to occur in the Milky Way.”
CONFIRMATION OF FAINT DWARF GALAXIES IN THE M81 GROUP (2013, background): “…1995; Mateo 1998; McConnachie & Irwin 2006; Simon & Geha 2007; Belokurov et al. 2007; Willman et al. 2005; Walsh et al. 2007; Zucker et al. 2006; Martin et al. 2006; Ibata et al. 2007; Irwin et al. 2008; McConnachie 2012) along with Centaurus and Hydra cluster members (Misgeld & Hilker 2011).”